Acquired Intangible Assets and Liabilities (Summary of Acquired Intangible Assets) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Below-market lease, gross amount	$ 442,936	$ 442,535
Below-market lease, accumulated amortization	(250,269)	(242,422)
Total	192,667	200,113
Acquired in-place lease value
Finite-Lived Intangible Assets [Line Items]
Intangible assets written off due to deconsolidation	120,000
Gross amount (1)	1,450,914	1,569,401
Accumulated amortization	(840,778)	(795,033)
Net	610,136	774,368
Tenant relationship value
Finite-Lived Intangible Assets [Line Items]
Intangible assets written off due to deconsolidation	375,000
Gross amount (1)	1,966,006	2,339,606
Accumulated amortization	(322,791)	(291,818)
Net	1,643,215	2,047,788
Acquired above-market leases
Finite-Lived Intangible Assets [Line Items]
Gross amount (1)	278,592	277,796
Accumulated amortization	(172,548)	(158,037)
Net	$ 106,044	$ 119,759